With glycerin as the plasticizer, the wood fiber as the reinforcement, corn starch as the substrate, PVA as binder, AC/ZnO as foaming agent, wood fiber reinforced corn starch composite materials were prepared by melt blending method. The influences of extrusion pressure, extrusion rate, heating temperature and moisture content on the composite foam’s foaming ratio were researched. The results showed that the expansion ratio of the composite materials firstly increased but then decreased later with the increase of extrusion pressure, when the extrusion pressure was 80 MPa, expansion ratio reached a maximum of 14.8. With the increase of extrusion rate, the change trend of material expansion rate was nonlinear, with the extrusion rate of 20 cm/s, expansion ratio reached a maximum of 14.8. With the increase of heating temperature, the expansion rate of the material firstly increased but then decreased later, and when heating temperature reached 135 ℃, expansion ratio reached a maximum of 13.8. The expansion rate of the material firstly increased but then decreased later with the increase of moisture content, and when the moisture content was 13%, foaming ratio reached a maximum of 13.8. Summarizing the mechanism and analyzing the changing curve of the related parameters and the foaming ratio were of great significance for optimizing the processing technology of materials.